(1) Field of the Invention
The present invention relates to a rotary compressor. More particularly, the present invention relates to a variable volume type of rotary compressor which is effectively used as a cooling medium compressor of a cooling system for an automobile.
(2) Description of the Prior Art
A rotary compressor, used for compressing a cooling medium in a cooling system for an automobile, is ordinarily connected to a crank pulley of an engine through an electromagnetic clutch and rotated in a relatively broad range of speeds from about 700 to about 6000 r.p.m.. The volume or capacity of the rotary compressor is predetermined primarily to produce a cooling effect which is sufficient even at a low rotational speed. Accordingly, when the speed of rotation is high, or the cooling load is low, the cooling capacity is then excessive.
If the cooling capacity is excessive, the suction side pressure of the rotary compressor is reduced, and, therefore, the compression ratio is reduced, resulting in a reduction of the efficiency of the rotary compressor and also in a decrease in the fuel efficiency of the automobile.
In conventional systems, cooling is adjusted by detecting the temperature in the driver's compartment of the car and selectively energizing an electromagnetic clutch in response to the detected temperature. However, if this method is adopted, the variations in the load of the engine are large, and it is therefore impossible to obtain good engine response while driving. In addition, since the compressor is intermittently operated, the temperature in the driver's compartment is always changing relative to a desired temperature and, as a result, a stable cooling effect cannot be obtained. When the rotary compressor is used for an air conditioner in a house, the problem of the varying degree of cooling due to the intermittent operation of the compressor similarly arises.
In the case of a rotary compressor of a cooling system for an automobile, the range of the rotation speed is very broad and there is a wide variation in cooling the driver's compartment, for example, from a high load condition in the middle of summer to a low load condition at the beginning of spring. Accordingly, in this field, there exists a need for a type of rotary compressor having a simple structure, in which the quantity of the cooling medium discharged from the compressor is changed within a broad range as gradually as possible.
It has been experimentally confirmed that when a rotary compressor is operated at the quantity smaller by about 20% than the maximum quantity, lubricating oil present in the cooler system stays in a condenser or receiver of the cooler system and is not supplied to the rotary compressor, with the result that the durability and efficiency of the rotary compressor is drastically reduced.
It is therefore an object of the present invention to provide a rotary compressor having a simple structure, in which the quantity of the cooling medium discharged from the compressor can be changed, within a broad range, as gradually as possible and in which reduction of the durability and efficiency can be prevented.